In a manufacturing process of a semiconductor device or an FPD (flat panel display), a plasma is often used in processes, e.g., etching, deposition, oxidation, sputtering and the like, in order to make a processing gas react efficiently at a relatively low temperature. Conventionally, a capacitively coupled plasma processing apparatus capable of generating a plasma of a large diameter is mainly used for a single-wafer plasma processing apparatus.
Generally, in the capacitively coupled plasma processing apparatus, an upper and a lower electrode are disposed in parallel with each other in a processing chamber as a vacuum chamber, and a substrate to be processed (e.g., a semiconductor wafer, a glass substrate or the like) is mounted on the lower electrode. By applying a high frequency power (an RF power) to both electrodes, electrons accelerated by a high frequency electric field formed between the electrodes, secondary electrons emitted from the electrodes, or heated electrons collide with molecules of a processing gas to generate ions. Accordingly, a plasma of the processing gas is generated, and a required microprocessing, e.g., etching, is performed on a substrate surface by radicals or ions in the plasma.
In the etching process, there is widely used a dual frequency application mode in which a relatively high frequency wave (generally greater than or equal to about 40 MHz) for plasma generation (discharge) and a relatively low frequency wave (generally lower than or equal to about 13.56 MHz) for ion attraction to the substrate (bias) are simultaneously applied to both electrodes.
Meanwhile, with increasing demands for miniaturization and high integration of devices in the semiconductor processing technique, a high efficiency, high density and low bias plasma processing is required in the capacitively coupled plasma processing apparatus. To do so, the high frequency wave for plasma generation tends to be set as high as possible. Meanwhile, along with the tendency to increase the chip size and the diameter of the substrate, the plasma is required to be of a larger diameter and, therefore, a chamber (processing vessel) is scaled up accordingly.
Here, the problem is that it is difficult to have a uniform plasma density in a processing space of the chamber (especially, in a radial direction). That is, when a discharging RF frequency increases, the profile of the plasma density becomes high at a central portion of the substrate and low at an edge portion thereof due to the wavelength effect causing formation of standing waves in the chamber and/or a skin effect making the high frequency wave be concentrated in the central portion on the electrode surface. The non-uniformity of the plasma density on the substrate leads to a non-uniformity of the plasma processing. As a consequence, the production yield of the semiconductor devices decreases.
To that end, various electrode structures have been developed. For example, in a plasma processing apparatus described in Japanese Patent Laid-open Application No. 2004-363552, uniformity in a plasma density distribution is improved by inserting a dielectric member in a main surface of an electrode facing a processing space so that an impedance to a high frequency power emitted from the main surface of the electrode to the processing space increases at a central portion of the electrode and decreases at an edge portion of the electrode.
The technique for inserting a dielectric member in a main surface of an electrode is disadvantageous in that the impedance distribution on the main surface of the electrode is fixed by a profile and a material of the dielectric member. Accordingly, a process region where the uniformity of the plasma density distribution can be controlled is small. Further, it is not possible to flexibly cope with various processes or changes of processing conditions.